1. Field of the Invention
This invention pertains to the general field of jet-powered watercraft. In particular, it provides a device for increasing the versatility of factory-installed propulsion and steering nozzles of small watercraft.
2. Description of the Related Art
Jet-propelled watercraft have recently become very popular for sport and entertainment because of their versatility and relatively simple construction. In particular, the type of craft designed for one-person use, often called "jet skis," have become as common at recreational water resorts as snowmobiles have been for years at winter resorts. The power units of these boats generally contain an internal combustion engine that drives a jet propulsion assembly consisting of an impeller housed in the rear portion of the hull. The impeller is rotatably journaled in a tunnel between a water inlet port and a discharge nozzle which provides both propulsion and steering to the craft. The nozzle is pivotally mounted on a support frame in the back of the craft and tied to control linkage that permits a user to vary the direction of the water jet, thus providing means for steering the unit. In addition, a mechanism for reversing the direction of flow of the water, such as a reverse-thrust bucket, is normally hingedly mounted on the nozzle of larger boats and controlled by a separate linkage system.
The prior art teaches many different variations of watercraft jet-propulsion nozzles which incorporate features for improving the performance of the watercraft. For example, U.S. Pat. No. 3,982,494, issued to Posti (1976), describes an auxiliary rudder for improving the lower-speed manuverability of a jet-powered craft. The rudder is coupled to the water pressure generated by the impeller so as to rise out of the water at high speeds, thus eliminating unwanted drag that would affect performance when the engine is under high load. The rudder is functional at low speeds only, when maneuverability is harder to achieve by jet propulsion alone and when the engine can afford the power loss resulting from the additional friction loss.
In U.S. Pat. No. 4,538,997 (1985), Haglund discloses a system of baffles incorporated in the body of the nozzle for providing varying degrees of back thrust. The invention is directed at overcoming the problem of conventional bucket-like thrust-reversing means which project beneath the hull and tend to slow down the watercraft.
U.S. Pat. No. 4,708,671 to Watanabe (1987) discloses another thrust-reversing device that is designed to permit the reversal of the direction of the water jet exhausted from the nozzle without protruding below the hull of the craft. This is achieved by adding channels in the bottom of the boat that conform with the curved ends of the device.
U.S. Pat. No. 5,049,096 to Henn (1991) describes an accessory attachment for conventional watercraft nozzles for increasing the directional control of the water jet and improving the fluid-flow characteristics of the jet. The device uses internal vanes to reduce the spiralling motion imparted by the impeller on the water jet and comprises a directional control to improve the side-to-side movement of the nozzle.
In U.S. Pat. No. 5,062,815 (1991), Kobayashi describes a drive control for effecting operation of a watercraft in either a forward or reverse drive mode while a rider is accommodated in a straddled position. In U.S. Pat. No. 5,067,918 (1991), the same inventor discloses a mechanism for deflecting the flow at the discharge nozzle to form a rooster-tail effect. The invention includes a modified reverse-thrust bucket with a clearance that permits the formation of the tail without affecting the reverse-thrust function of the unit.
Finally, French Patents No. 1,338,139 (1963) and No. 1,342,642 (1963), issued to Dowty Technical Development Limited, French Patent No. 1,492,084 (1967), issued to Perrier et al., and German Patent No. 2,242,320 (1973), issued to Smith, all describe various apparatus for improving the performance of watercraft jet-propulsion systems.
These prior-art devices are designed primarily to reduce drag and increase maneuverability by providing improved directional flow of the water jet. None of them have a direct affect on the pressure or velocity of the jet stream, which remain controlled only by the impeller's speed. Although many different approaches have been adopted in the referenced disclosures, none is directed at improving the performance of jet nozzles by providing a variable cross-section exhaust duct. In fact, manufacturers systematically choose the nozzle aperture's size to best balance the top- as well as the bottom-end speed of the craft. Since the performance of the impeller is greatly affected by small variations in the cross-section of the nozzle's outlet orifice, providing an adjustable aperture is an effective means for adding flexibility to the conventional control systems of small watercraft.
Therefore, there remains a need for an improved water-jet nozzle that permits a user to continuously vary the size of the nozzle's orifice during operation, thus providing an added degree of flexibility in controlling the maneuverability and performance of the watercraft. The present invention describes such a device as an accessory attachment for conventional nozzles.